Oil seals are widely used as essential machine elements in the fields of vehicles, industrial machines, etc. In recent years, there is an increasing demand for eco-friendly vehicles and like products that are fuel-efficient and low resistant. Oil seals used in various machines are also required to have less friction.
Conventionally, friction was reduced by applying coating or PTFE sintering to oil seal surfaces; however, according to this method, it was necessary to add a coating or sintering process to the production process of oil seals, which caused a problem of increased cost. Further, it was difficult to apply them to some oil seals, depending on their shape. Alternatively, it is also possible to seek less friction by means of the shape and structure thereof; however, this may cause a problem of reduced sealing properties due to a decrease of interference, etc.
The present applicant has proposed various fluororubber compositions in which fluororubber is blended with fillers having specific shapes so as to improve their sealing properties and impact-absorbing properties, etc.
Patent Document 1 discloses a fluororubber composition comprising fluororubber and potassium titanate whisker having an approximate composition K2O.(TiO2). (n: an integer of 1 or more, preferably 4 to 8) and generally having an average fiber length of about 10 to 20 μm and a fiber diameter of about 0.2 to 0.5. This fluororubber composition has improved material strength and abrasion resistance, and can be suitably used as a molding material for rotating seals, reciprocating seals, and the like.
Patent Document 2 discloses an oil seal for forward/reverse rotation comprising fluororubber, and wollastonite produced in the U.S. or Mexico, or potassium titanate whisker having an aspect ratio of 8 or more. This oil seal can continuously seal fluid well in forward/reverse rotation movement, even under relatively high temperature conditions (e.g., a service condition temperature of 100 to 200° C.).
The Examples of Patent Document 2 use wollastonite having an aspect ratio of 8 (fiber length: about 32 μm, fiber diameter: 4 μm), 13 (fiber length: 65 μm, fiber diameter: 5 μm), or 17 (fiber length: 136 μm, fiber diameter: 8 μm), and the Comparative Example uses wollastonite having an aspect ratio of 5 (fiber length: 35 μm, fiber diameter: 7 μm).
Patent Document 3 discloses a fluororubber composition suitable for rotary sliding seal applications with the aim to reduce torque (reduction in friction), to improve the initial characteristics of sealing properties by reducing oil leakage (measuring the amount of oil pumping with sliding of the seal member as the time from the supply of oil to the termination of inlet), and to suppress the degradation of the characteristics after friction and abrasion occur. The fluororubber composition comprises a fluororubber blended product of polyol-crosslinkable fluororubber and peroxide-crosslinkable fluororubber, and a polyol-based crosslinking agent or a mixture of a polyol-based crosslinking agent and a peroxide crosslinking agent, depending on the blending ratio.
Patent Document 3 indicates that the fluororubber composition may suitably contain, as rubber compounding agents, a reinforcing agent, such as carbon black or carbon fibers; a filler, such as hydrotalcite, calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, aluminum silicate, magnesium silicate, calcium silicate, potassium titanate, titanium oxide, barium sulfate, aluminum borate, glass fibers, aramid fibers, diatomaceous earth, or wollastonite; and the like. The Examples of Patent Document 3 uses wollastonite (fiber length: 35 μm, fiber diameter: 7 μm).
Patent Document 4 discloses a fluororubber vulcanization-molded product comprising fluororubber and a filler having a specific shape, wherein the product has a slight increase in hardness and has excellent impact-absorbing properties and non-adhesiveness. Patent Document 4 indicates that the filler having a specific shape is a filler having an average particle diameter of 1 to 50 μm, preferably 5 to 30 μm, and an aspect ratio of 5 or more, or a fibrous or needle-like filler having an average fiber length of 1 to 500 μm, preferably 5 to 200 μm.
As the filler to be blended with the fluororubber, Patent Document 4 refers to calcium carbonate, aluminum silicate, magnesium silicate, wollastonite (calcium silicate), xonotlite (calcium silicate), talc, mica, sericite, glass flakes, various metallic foils, graphite, plate-like iron oxide, plate-like calcium carbonate, plate-like aluminum hydroxide, glass fibers, carbon fibers, aramid fibers, vinylon fibers (PVA fibers), alumina fibers, metal fibers, plaster fibers, phosphate fibers, dawsonite, aluminum borate, potassium titanate, needle-like magnesium hydroxide, and the like. As the fibrous filler, Patent Document 4 refers to glass fibers, carbon fibers, aramid fibers, vinylon fibers, alumina fibers, metal fibers, and the like. As the needle-like filler, Patent Document 4 refers to potassium titanate, wollastonite, zonolite, phosphate fibers, plaster fibers, dawsonite, aluminum borate, needle-like MgO, magnesium hydroxide, calcium carbonate, aluminum silicate, magnesium silicate, and the like.
The Examples of Patent Document 4 use calcium silicate (average diameter: 3 μm, average length: 25 μm), carbon fibers (average fiber diameter: 15 μm, average fiber length: 150 μm), or calcium carbonate (average particle diameter: 1 μm, average length: 5 μm).